From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95EA4C47256 for ; Wed, 6 May 2020 15:57:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 734AC20708 for ; Wed, 6 May 2020 15:57:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="KBqROWa/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729667AbgEFP5Q (ORCPT ); Wed, 6 May 2020 11:57:16 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:43895 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729883AbgEFP5Q (ORCPT ); Wed, 6 May 2020 11:57:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588780634; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cmGtqLKbdcuk3GEDBRY8pjioOEUIcpSAuT0yu/iJDjA=; b=KBqROWa/+HYK8S/pl/UXzgs/ruLAt5G1rS6SP2znlOxdb0XU4f+skW7oCHnPQuY/pFmz7m j9qERethcXBwPsZqqvPhgCr+syUy2zjqmHOUAKQD7q9H/kXiLpEzj84W0ssmk2VqCix3JQ HVLQihxoJImYame7pLHAjWGMGgzrl0g= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-468-g6fqxtzTPAayF5gxIhVxvw-1; Wed, 06 May 2020 11:57:11 -0400 X-MC-Unique: g6fqxtzTPAayF5gxIhVxvw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5446B185547A; Wed, 6 May 2020 15:57:09 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2239860BEC; Wed, 6 May 2020 15:57:09 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id 046Fv8iW018222; Wed, 6 May 2020 11:57:08 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 046Fv8dP018219; Wed, 6 May 2020 11:57:08 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Wed, 6 May 2020 11:57:08 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Greg Kroah-Hartman cc: Richard Henderson , Ivan Kokshaysky , Matt Turner , linux-alpha@vger.kernel.org, Sinan Kaya , Arnd Bergmann , linux-serial@vger.kernel.org, linux-rtc@vger.kernel.org Subject: Re: [PATCH 2/2 v2] alpha: add a delay before serial port read In-Reply-To: <20200506154938.GA3537174@kroah.com> Message-ID: References: <20200506114711.GB3024358@kroah.com> <20200506154938.GA3537174@kroah.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-rtc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org On Wed, 6 May 2020, Greg Kroah-Hartman wrote: > On Wed, May 06, 2020 at 11:29:29AM -0400, Mikulas Patocka wrote: > > > > > > On Wed, 6 May 2020, Greg Kroah-Hartman wrote: > > > > > > Index: linux-stable/drivers/tty/serial/8250/8250_port.c > > > > =================================================================== > > > > --- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 08:25:19.000000000 +0200 > > > > +++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 09:04:17.000000000 +0200 > > > > @@ -442,6 +442,10 @@ static unsigned int mem32be_serial_in(st > > > > > > > > static unsigned int io_serial_in(struct uart_port *p, int offset) > > > > { > > > > +#ifdef CONFIG_ALPHA > > > > +/* we need a small delay, the Alpha Avanti chipset locks up with back-to-back accesses */ > > > > + ndelay(300); > > > > +#endif > > > > > > We really do not like #ifdef in .c files, especially ones that cause a > > > coding style violation :) > > > > > > Why can't you do this as a quirk for this specific chipset? You should > > > tie it to the serial port hardware type, not to the CPU type. > > > > > > thanks, > > > > > > greg k-h > > > > Do you want this patch? It enables the delay based on the specific PCI-ISA > > bridge. > > > > There is still "#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI)" because > > if we want to reference a variable defined by the PCI subsystem in the > > arch/alpha tree, we must do it conditionally. If you want to get rid of > > these #ifs, please describe how. > > > > Mikulas > > > > > > From: Mikulas Patocka > > > > The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder > > barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on > > the Alpha Avanti platform. > > > > The patch changes timing between accesses to the ISA bus, in particular, > > it reduces the time between "write" access and a subsequent "read" access. > > > > This causes lock-up when accessing the real time clock and serial ports. > > > > This patch fixes the serial ports by adding a small delay before the "inb" > > instruction. > > > > Signed-off-by: Mikulas Patocka > > Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2") > > Cc: stable@vger.kernel.org # v4.17+ > > > > --- > > arch/alpha/include/asm/pci.h | 2 ++ > > arch/alpha/kernel/pci.c | 4 ++++ > > drivers/tty/serial/8250/8250_core.c | 7 +++++++ > > drivers/tty/serial/8250/8250_port.c | 3 +++ > > include/linux/serial_core.h | 1 + > > 5 files changed, 17 insertions(+) > > > > Index: linux-stable/include/linux/serial_core.h > > =================================================================== > > --- linux-stable.orig/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200 > > +++ linux-stable/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200 > > @@ -154,6 +154,7 @@ struct uart_port { > > > > /* quirks must be updated while holding port mutex */ > > #define UPQ_NO_TXEN_TEST BIT(0) > > +#define UPQ_DELAY_BEFORE_READ BIT(1) > > > > unsigned int read_status_mask; /* driver specific */ > > unsigned int ignore_status_mask; /* driver specific */ > > Index: linux-stable/drivers/tty/serial/8250/8250_core.c > > =================================================================== > > --- linux-stable.orig/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200 > > +++ linux-stable/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200 > > @@ -37,6 +37,9 @@ > > #ifdef CONFIG_SPARC > > #include > > #endif > > +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI) > > +#include > > +#endif > > Don't need the #if for this. You're right. > > #include > > > > @@ -490,6 +493,10 @@ static void univ8250_rsa_support(struct > > static inline void serial8250_apply_quirks(struct uart_8250_port *up) > > { > > up->port.quirks |= skip_txen_test ? UPQ_NO_TXEN_TEST : 0; > > +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI) > > + if (alpha_serial_port_needs_delay) > > + up->port.quirks |= UPQ_DELAY_BEFORE_READ; > > +#endif > > Why is a #define needed here? > > You can do this same type of change without any #ifdefs in any .c files > and that would be much nicer. Because alpha_serial_port_needs_delay is defined only on Alpha - so we need to guard accesses to it with #ifdef CONFIG_ALPHA - otherwise the kernel wouldn't link on non-Alpha platforms. Should I make it defined for all architectures? Mikulas